1. Field of the Invention
The present invention relates to a pump unit including a pair of hydraulic pump main bodies and a pair of trunnion type movable swash plates which vary supply and discharge oil volume of a pair of pump main bodies.
The present invention also relates to a pump unit including a housing whose oil-storable inner space is divided into a pump accommodating chamber and a gear accommodating chamber.
2. Background Art
A pump unit including multiple pump shafts, multiple hydraulic pump main bodies driven by each of the multiple pump shafts, a housing which accommodates the multiple hydraulic pump main bodies and at the same time supports the multiple pump shafts, and multiple movable swash plates which vary suction/discharge oil quantity has been popularly used in various fields such as working vehicles, etc. (for example, see Japanese Patent Application Laid-open No. 2003-291674).
Now, for the movable swash plate, in general, a trunnion type movable swash plate and a cradle type movable swash plate exist.
The trunnion type movable swash plate has a pair of shafts and a swash plate located between the pair of shafts, and since there is no need to provide a swash plate receiving portion that slidably holds the swash plate, no large force is required for operation but at the same time, a construction to support the pair of shafts at both ends thereof must be equipped to the housing, the trunnion type movable swash plate has a disadvantage of increasing the size of the housing.
In addition, the housing is in general configured to store oil so that the multiple hydraulic pump main bodies are cooled by oil introduced, but no thoroughgoing consideration was made for improving the capability of cooling the hydraulic pump main body by circulating oil inside the housing.
The present invention has been made in view of the foregoing conventional technique and it is one of the objects of the present invention to provide a pump unit including a pair of hydraulic pump main bodies, a pair of trunnion type movable swash plates that vary the suction/discharge oil quantity of the pair of hydraulic pump main bodies, respectively, and a housing that can store oil and accommodates the pair of hydraulic pump main bodies, the pump unit improving the cooling efficiency of the hydraulic pump main body by the oil introduced into the housing while preventing an increase of the housing size.
In addition, a pump unit having a housing whose oil-storable inner space is divided into a pump accommodating chamber for accommodating a hydraulic pump main body and a gear accommodating chamber for accommodating a gear train has been used in various fields such as working vehicles, etc. (for example, see Japanese Patent Application Laid-open No. 2003-291674 mentioned above).
Such a conventional pump unit is useful in that the inner space of the housing can be used as oil storage and at the same time the hydraulic pump main body can be cooled by the stored oil while entry of impurities such as iron powder, etc. generated from the gear train into the pump accommodating chamber can be prevented or reduced.
However, for the conventional pump unit, thoroughgoing consideration was not made on improving the cooling efficiency of the hydraulic pump main body by circulating the stored oil inside the housing.
In addition, the oil stored in the housing gives rise a rotational resistance against rotating bodies such as the gear train, hydraulic pump main body, and so on.
With respect to this point, thoroughgoing consideration is not given to conventional pump units, either.
The present invention is made in light of the above-mentioned conventional technique, and it is another object of the present invention to provide a pump unit which is equipped with a housing whose inner space is designed to store oil, the pump unit preventing stagnation or pooling at the same position of oil stored in the housing and improving the cooling efficiency of the pump main body contained in the housing.
It is still another object of the present invention to improve the transmission efficiency of the gear train as much as possible by reducing the rotational resistance against the gear train due to the stored oil, while the above-mentioned object is being obtained.